74 dodge dart tranny issues

DUH!! I don't know how I thought you have a 3 speed manual but somehow I got mixed up. Must have been the cold medicine with Codeine. LOL

Ignore my other replies cause I was thinking you had a manual trans. If and automatic looses pressure and drops out of gear going down the road that's not good at all. You can try a new filter and fluid as 70AAR said and see what happens. If that don't help it's time to rebuild it.

Never swapped to a 4 spd so I can't say how much work it is but I'm sure it'll cost you allot cause A-body 4 speeds transmissions are pretty pricey. Then you need a shifter and linkage, bellhousing, pressure plate, clutch, different driveshaft, and pedal and linkage assemblies. Probably some other things I'm forgetting too.